The present invention refers to the area of chemistry, in particular to materials of catalytic interest
The present invention deals with a pillared mixed oxide that maintains a separation between sheets, there being individual structural layers, that have microporous channels and cavities.
Laminar materials such as clays, phosphates, hydroxycarbonates, silicic acids (kanemite, magadiite, keniaite, etc.), transition metal sulfides, graphite, laminar hydroxides and others, are capable of swelling in the presence of water and/or suitable interlaminar cations. The individual sheets of these materials are kept together by means of weak hydrogen bond type forces and/or electrostatic interactions. These bonds break easily when the intercalation force or the solvation energy of the cations are greater than the interlaminar attraction forces.
The interest of swollen materials is to make the interlaminar space accessible to the reacting molecules, and consequently, the inside surface, considerably increasing the active surface accessible to the reagent. When the material intercalated between the sheets of the mixed oxide is eliminated by calcination, the swollen laminar compound collapses, recovering the original interlaminar distance.
In order to prevent the interlaminar collapse, intercalation of the xe2x80x9cpillarsxe2x80x9d comprised of thermally stable inorganic oxyhydroxides in the swollen material has been proposed. These xe2x80x9cpillarsxe2x80x9d are comprised of polymeric hydroxides of Al, Si, Cr, Ni, Zr, etc. . . . , which after calcination treatment give rise to columns of the corresponding oxide that are anchored in the surface of the sheets keeping them separated and stabilizing the final pillared product.
It is an object of the present invention to provide a pillared material consisting of a mixed oxide, which maintains a separation among sheets, appearing isolated structural layers with channels and microporous cavities, and which may be used as catalyst in acid catalyzed reactions.
It is an additional object of the present invention a method for preparing the laminar solid and the subsequent treatment thereof, until a highly accessible microporous pillared material with acid characteristics capable of being used as a catalyst is obtained.
It is an additional object of the invention the use of the pillared microporous material in acid catalyzed reactions, such as cracking and isomerization of organic compounds, and preferably of hydrocarbons, as well as in hydroisomerization and hydrocracking processes.
It is a further object of the invention to provide catalytic compounds which comprise the pillared micro- or mesoporous material and a matrix and their use in processes of dewaxing and isodewaxing.
Finally, it is an additional object of the invention catalytic compositions which comprise the pillared micro- or mesoporous material and a hydrogenating function.
The present invention refers to an oxide which is a pillared material, called ITQ-36, with a micro- and mesoporous structure and a high external surface area, capable of supporting Brxc3x6nsted and Lewis acid centers and that is characterized by its X-ray diffractogram and its adsorption and catalytic properties.
The material ITQ-36 has a chemical composition represented by the formula
(XO2)n(Y2O3)m(H2O)p
wherein X represents, at least, a tetravalent element and Y represents, at least, a trivalent element, the atomic ratio between X and Y being at least 5. In preferred embodiments the atomic ratio between X and Y is higher than 10, or even higher than 30. In a more preferred embodiment said atomic ratio is higher than 30, or even higher than 40. Suitable limits for said atomic ratio may be between 30 and 500.
Preferably, X in XO2 represents, at least, a tetravalent element selected from among silicon, germanium and, more specifically silicon, in some cases it being able to also be titanium.
Preferably, Y in Y2O3 represents, at least, a trivalent, element, selected from among aluminum, iron, chromium and gallium, and more specifically aluminum.
The material ITQ-36 has an X-ray diffraction diagram with basal spacings and relative intensities summarized in Table 1.
In this description, and unless it is specified otherwise, the relative intensities of the X-ray diffraction peaks will be represented with the symbols and meaning established hereinafter:
The preparation process of the pillared oxide ITQ-36 consists of:
a first step comprising the synthesis of a precursor which is a laminar material that can be swollen,
a second step wherein the laminar material obtained is swollen by mixing the same with a swelling solution resulting in a swollen laminar material, which is a swollen laminar mixed oxide,
a third step wherein the swollen laminar material is washed and dried giving rise to a swollen dried laminar material, and
a fourth step wherein the swollen dried laminar material is pillared, washed, dried and calcined, to obtain the pillared mixed oxide, ITQ-36, of the invention.
In the first step the synthesis of a solid which is a laminar material, is carried out by mixing in an autoclave a source of a tetravalent element, which in the case of silicon may be for example a silica source such as AEROSIL, LUDOX, CABOSIL, tetraethylorthosilicate (TEOS) or any other known; a source of a trivalent element, which in the case of aluminum may be a source selected among boehmite, pseudoboehmite, Al2(SO4)3, AlCl3, Al(NO3) or any other one; a fluoride salt and a fluoride acid such as for example ammonium fluoride and hydrogen fluoride; an organic compound such as 1,4-diaminobutane, ethylendiamine, 1,4-dimethylpiperazine, 1,4-diaminocyclohexane, hexamethylenimine and pyrrolidine, preferably, 4-amino-2,2,6,6-tetramethylpiperidine; and water in suitable proportions.
Synthesis of said solid material takes place at temperatures between 100 and 200xc2x0 C., with permanent stirring of the gel and a duration between 1 and 30 days and, preferably between 1 and 18 days, and more preferably between 2 and 12 days. After this time the reaction product, a white solid with a pH between 9 and 10 is washed with distilled water, filtered and dried.
During the second step swelling of the obtained solid material takes place by preparing a suspension thereof in a solution that we will call the xe2x80x9cswellingxe2x80x9d solution, formed by an organic compound of a long hydrocarbonated chain that has a proton acceptor group, such as for example a quaternary alkylammonium, an amine, or an alcohol with more than three carbons in the chain, to which a controlled amount of a compound capable of providing OHxe2x88x92 to the reaction medium, such as for example, a quaternary alkylammonium hydroxide is added, until a pH higher than 10 is obtained. The organic compound used as a OHxe2x88x92 source may be any amine or quaternary alkylammonium compound, preferably cetyltrimethylammonium hydroxide (CTMA+OHxe2x88x92).
The swelling solution prepared is mixed with the previously described solid material of the first step in a weight ratio of swelling solution to solid laminar material between 4 and 200. The resulting suspension is kept under reflux and permanent stirring between 20 and 200xc2x0 C., and preferably between 40 and 120xc2x0 C., for a time no less than 1 hour until the swollen laminar material is obtained.
During the third step the swollen laminar material is thoroughly washed with distilled water and dried at temperatures lower than 300xc2x0 C. and preferably lower than 150xc2x0 C. A swollen dried laminar material is thus obtained.
Once washed and dried, the swollen dried material has a characteristic X-ray diffraction diagram whose basal spacings and relative intensities are summarized in Table 2.
Then the pillaring process is proceeded with during the fourth step. For this purpose, a suspension of swollen dried material in a pillaring agent, preferably tetraethylorthosilicate (TEOS) is prepared, in a variable weight proportion between 2 and 20. This suspension is kept under reflux and constant stirring, at a temperature between 30 and 150xc2x0 C., and preferably between 50 and 80xc2x0 C., for a time no less than 1 hour and with permanent nitrogen flow until the pillared material is obtained.
During the fourth step the obtained pillared material is washed and dried at temperatures lower than 300xc2x0 C. Once dry, it is calcined at temperatures between 300 and 800xc2x0 C. and, preferably between 400 and 600xc2x0 C. giving rise to the product ITQ-36.
Pillaring agents include polymeric oxides of elements of group IVA of the Periodic Table of the elements, such as silicon, germanium or tin, or of group IVB such as titanium, zirconium, etc., although pillars that include polymeric silica are usually chosen. The pillaring oxides could also include an element that provides catalytically active acid sites in the pillars, preferably aluminum, gallium, rare earth or mixtures thereof.
ITQ-36 has, together with its laminar nature and X-ray diffractogram, some characteristic textural properties as a result of having a microporous part, and a high external surface area as a result of the cavities formed by the intercalation of pillars between the sheets. Hence, Table 3 summarizes the values obtained for a sample of ITQ-36 by applying the BET equation to the nitrogen adsorption isotherm at the temperature of liquid nitrogen.
The material ITQ-36 may undergoes a subsequent hydrothermal calcination step or a post-calcination in the presence of fluorine or a fluorine compound, or treatment with a phosphorous compound.
This material ITQ-36 is capable of being used as a catalyst in acid catalysis reactions such as cracking and isomerization of organic compounds, and preferably of hydrocarbons, as well as in hydroisomerization and hydrocracking for which a hydrogenating-dehydrogenating function such as for example platinum, palladium, nickel, rhodium, ruthenium or mixtures thereof is introduced together with the acid function.
The invention also refers to a catalytic composition that comprises an oxide material as ITQ-36 and a hydrogenating function such as Pt, Pd, Ru, Ni, Co, Mo, V, W, Rh or any of the combinations thereof, whether they are deposited on the oxide material or on a high surface support such as alumina, silica or silica-alumina.
The invention further refers to the use of a catalytic composition as defined in the preceding paragraph in a process for the isodewaxing of paraffins that comprises contacting the hydrocarbon feed together with hydrogen at temperatures between 250 and 400xc2x0 C., at pressures between 10 and 90 atmospheres, with the catalytic composition, as well as the use of said catalytic composition as a dewaxing catalyst.
The invention additionally refers to a catalytic compound formed by an oxide material as ITQ-36 and a matrix, which may be a refractory oxide.
The invention also refers to the use of said catalytic compound in a process for the catalytic isomerization of n-butenes in isobutenes that involves contacting the hydrocarbon with the catalytic compound, at temperatures between 300 and 500xc2x0, as well as the use of said catalytic compound in a hydrocarbon cracking process that comprises contacting the hydrocarbons with said catalytic compound, at temperatures higher than 400xc2x0 C. and that may or may not be in the presence of steam.